HCI Standards: Bases and Examples

Contents of this page:

This page provides some examples of HCI design recommendations that often
appear in standards and that are based on human physical, cognitive, and
affective characteristics.

Physical factors

Some of the recommendations in standards for software HCI are based
on the physical attributes of human beings. (Hardware standards, on the
other hand — screen reflectivity, for example, or the force required
to press a key or mouse button — have a much stronger physical basis.
This discussion addresses only software HCI.)

Here are two examples of physically based HCI recommendations:

Saturated red text
on a saturated blue
background — a no-no

Avoid displaying saturated
red text on a saturated blue background (or
vice versa). A condition called "chromostereopsis" makes the text extremely
difficult to read for most people (example at right). The eye, you see, focuses
different wavelengths of light (i.e., colors, whence "chromo") differently.
(So does a camera's lens, for that matter, and in fact a few "apochromatic" lenses
are designed to counteract this.) Anyway, when red is in focus, blue
appears ever-so-slightly fuzzy, and vice versa. This makes red and
blue seem to be at different distances (whence "stereo") from the viewer's
eye (whence "opsis"). (Note: Green is almost as bad as blue.)

Use motion only for getting and keeping the
user's attention. Peripheral vision is more sensitive to motion (e.g., animation and
blinking) than is foveal vision -- i.e., movement that you see out
of the corner of your eye will tend to distract you from anything else
on the screen. (I'm not showing an example of this because I want you
to read this page. But just look at any web page with an animated ad
banner, and notice how hard it is to keep your eyes on the page content.
And you know they want your attention!)

Physically based recommendations tend to be stronger advice than cognitively
or affectively based ones because the relevant characteristics vary less
from person to person. You and I may have rather different likes or learning
styles (you may even be a Windows fan, heaven help us!), but virtually
everyone with normal color vision experiences chromostereopsis in looking
at red on blue.

Cognitive factors

There are so many recommendations based on cognitive factors that I
had trouble deciding which ones to choose. Anyway, here are two:

When listing options for user selection (e.g.,
in a menu or list box), present them in an order that makes sense
to the user's task, grouping them if there are more than just a few.
If there is no logical order, list the options alphabetically. For example, a File menu
has New and Open together, Page Setup and Print together, and Quit
at the bottom (except in Claris Home Page, which
lists the ten most recently used files at the bottom, below Quit),
while a font list shows the available fonts in alphabetical order
by name. This recommendation takes advantage of the user's understanding
of the task or of some other organizing principle and facilitates
finding items in the list.

Provide keyboard mechanisms ("shortcuts" or "accelerators")
for commonly used functions and menu items. This allows users
who become familiar with the product to use the keyboard for what
may be faster access to those functions.

Affective factors

Affect (pronounced af'fect) is, essentially, subjective reaction.
It includes emotions, values, preferences, satisfaction — all the stuff
it's so hard for many of us to get a handle on. But if we want our users
to be satisfied with our products, we have to pay attention to it. Here
are two examples of recommendations based on considerations of user affect:

Design to put users in control of the interaction. For example
avoid giving the impression that the computer is telling them what
to do, and do not use loaded words such as "illegal" in error messages. (Nobody is going to jail for spelling a command name wrong.)

Provide for some user customization of the æsthetics of
the interface. Examples include Macintosh Appearance controls,
Windows Schemes, and Motif Palettes.